An aunt told me once that an easy way to break a dog of digging is to bury a balloon. when it pops, it usually ends the digging.

Bury a balloon? How many balloons does one have to bury? What if the dog just decides to dig to China in no particular place? Dogs dig to DIG. It is instinctual, particularly in terriers. There's not much in the way of "control" that you can muster except to call your local animal control organisation. A dog at large won't be around too long, however. They are usually hit by cars. Sadly, it is the dog who pays for the owners ignorance.

Here is a link that might be useful: My Name Is Sam

Not sure what size of area you are wanting to control but there is a battery powered ultrsonic device that works for dogs, I have enclosed a link for you to check out.

Here is a link that might be useful: Animal Away